The invention relates to vulcanizable elastomeric roof sheeting or flashing compositions containing vulcanizable elastomers and metallurgical carbon. More particularly, the invention relates to vulcanizable elastomeric roof sheeting or flashing compositions which comprise a vulcanizable elastomer, a metallurgical carbon and a vulcanizing agent.
Elastomeric roof sheeting, also referred to as roofing membranes, are known for use as roofing materials, particularly as single ply rubber roofing membranes for industrial and commercial flat roofs. These membranes are generally applied to the roof surface in the vulcanized or cured state. Elastomers which are most commonly employed in forming the membranes are EPDM, butyl and neoprene but chlorosulfonated polyethylene and chlorinated polyethylene are occasionally utilized in some special applications. The roofing membranes are generally prepared by calendering the unvulcanized elastomer compounds into sheets of various widths, lengths and thickness and then vulcanizing the sheets usually employing hot air or steam autoclave, although continuous vulcanization is reported to be beyond the research phase.
Elastomeric roof flashing is also known for its use on roofs, especially flat roofs. This material is employed to seal around elements that extend or protrude from the roof surface such as sky lights, air conditioning units, vent pipes and the like. The elastomeric flashing compound is often formulated using the same elastomers as are employed in the roof sheeting compound but a special curing package is included in the compound which allows it to cure over an extended period of time under ambient temperature conditions. Thus, the roof flashing is applied to the roof surface in the unvulcanized state and cures in-situ on the roof.
Vulcanizable elastomeric EPDM and butyl compositions containing conventional carbon blacks and vulcanizing agents have long been known in the tire and industrial rubber products arts. More recently, vulcanizable EPDM and/or butyl rubber compositions have been proposed for use as roof sheeting and flashing compositions as illustrated by U.S. Pat. Nos. 4,461,875 and 4,514,442.
The aforementioned patents relate to roof sheeting and flashing compositions which comprise an elastomer selected from the group consisting of EPDM, butyl rubber and an EPDM-butyl rubber mixture; from 0.1 to 3.0 parts of a compound having the structural formula [(CH.sub.2).sub.n NCS].sub.2 S.sub.6 wherein n is 4 or 5; and 0 to 5.0 parts of a sulfur donor curative. The patents further disclose that the compositions may additionally contain one or more vulcanizing accelerators, processing oils, plasticizers and fillers and reinforcing agents. Among the fillers and reinforcing agents which are said to be especially useful are carbon black, silicates, talc, calcium carbonate and the like.
Elastomeric EPDM roofing compositions, especially compositions for roof sheeting or membranes, have rapidly gained acceptance in the commercial roofing industry due to the outstanding weathering resistance and flexibility of EPDM elastomers. However, the increased acceptance of elastomeric EPDM roofing compositions by the commercial roofing industry has been accompanied by increased cost competition. Accordingly, those active in the elastomeric EPDM roofing composition field are constantly striving to develop lower cost compositions. However, it has proven difficult to develop lower cost EPDM roofing compositions which do not involve some sacrifice in the important properties of the composition such as weathering resistance, flexibility and tear resistance. Thus, the development of low cost elastomeric roofing compositions having desirable physical properties is an important objective.